Apparatus and method for storing two-phase liquids

ABSTRACT

A method and apparatus for storing two-phase liquids of different densities in a storage tank whereby the higher density liquid may be drained from the tank and the change in densities when the lower density liquid appears is sensed thus, automatically stopping the draining off of the liquids.

United States Patent [1 Phillips 1 July 3,1973

APPARATUS AND METHOD FOR STORING TWO-PHASE LIQUIDS [75] Inventor: Ross E. Phillips, Pasadena, Tex.

[73] Assignee: Shell Oil Company, New York, N.Y.

[22] Filed: Nov. 5, 1970 [21] Appl. No.: 87,220

[52] US. Cl. 137/172 [51] Int. Cl F16t H00 [58] Field of Search 137/172 [56] References Cited UNITED STATES PATENTS 2,325,925 8/1943 Waugh 137/172 X 2,806,896 9/1957 Streuber 137/172 X Primary ExaminerAlan Cohan Attorney- T. E. Bieber and Harold L. Denkler [57] ABSTRACT A method and apparatus for storing two-phase liquids of different densities in a storage tank whereby the higher density liquid may be drained from the tank and the change in densities when the lower density liquid appears is sensed thus, automatically stopping the draining off of the liquids.

6 Claims, 1 Drawing Figure PAIENIEDJIIL3 ma mm a K .x I 0N INVENTOR. R. E. PHILLIPS APPARATUS AND METHOD FOR STORING TWO-PHASE LIQUIDS BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to liquid storage tanks, and, more particularly, to a method and apparatus for storing liquids of different densities in a manner permitting the drawing off of one of the liquids with a minimum amount of attendance.

2. Description of the Prior Art It is common practice to store liquids in storage tanks until it is desirable to use the liquids contained therein. However, in the storing of two-phase liquids such as water and hydrocarbon, the liquids tend to separate forming a layer of emulsion and water at the bottom of the stored hydrocarbon. This layer of emulsion and water must be removed to prevent process upsets and product contamination. Present practices involve the opening of a valve and draining the liquids into a sewer or the like with the operator doing the draining remaining in attendance so as to close the valve when the hydrocarbon begins to drain from the tank. Thus, the draining of such storage tanks depends upon the vagaries of operator interpretation for evaluation of the drained liquid. Also, contamination may be released both to the surface and to sub-surface sewers and collection systems resulting in possible pollution of the refinery environment.

SUMMARY OF THE INVENTION It is an object of this invention to provide a method and apparatus for storing liquids of different densities in storage tanks whereby the higher density liquid may be automatically drained from the storage tank with a minimum of attention.

his a further object of this invention to provide an apparatus and method for draining such liquids with a minimum waste of the lower density liquid. It is a still further object of this invention to provide an apparatus and method for reducing the amount of contaminate released to both the surface and to sub-surface sewers and collection systems in the draining of liquids from storage tanks thereby reducing the potential for pollution of the environment.

These and other objects are preferably accomplished by storing two-phase liquids of different densities in a storage tank in a manner whereby the higher density liquid may be drained from the tank and the change in densities when the lower density liquid appears is sensed thus automatically stopping the draining off of the liquids.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a vertical sectional, partly-schematic view of preferred apparatus for carrying out the techniques of my invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, a storage tank is shown containing therein at least two liquids l1 and 12. Although the tcchniques of my invention are applicable to any two-phase liquids of different densities, the invention will be described hereinbelow, but is not limited to, with regard to the storing of hydrocarbons. Thus, liquid 11 may be a higher density liquid such as water (which may include bottom sediment therein) and a liquid 12 may be a lower density liquid such as hydrocarbon.

A suitable drain 13 is associated with the bottom wall 14 of tank 10 for draining liquids therefrom. Although drain 13 may be located at any point on tank 10, it is preferably located adjacent the bottom thereof and preferably in contact with bottom wall 14 so as to be in a position to drain off as much of liquid 11 as possible from tank 10. Further, the configuration of drain pipe 15, in liquid communication with drain 13, is a matter of choice, the only requirement being that, for the purposes of my invention as will be discussed further hereinbelow, it discharge below the liquid level of tank 10. A suitable normally closed control valve 15 may be associated with drain pipe 15.

Thus, drain pipe 15 preferably includes a first generally vertical portion 16 extending downwardly from drain 13 and a second generally horizontal portion 17 extending generally parallel to the bottom wall 14 of tank 10.

A conventional automatic shut-off nozzle 18 is in liquid communication with drain pipe 15, as by connection to portion 17. Any standard nozzle may be used, such as those normally associated with gasoline pumps. For example, the OPW Automatic Nozzle manufactured by the Dover Corporation, OPW Division, of Cincinnati, Ohio, may be used. However, any suitable automatic shut-off nozzle which automatically shuts off upon the back-up of liquid therethrough may be used and such nozzle forms no part of the teachings of my invention. Further illustration thereof would also appear to be unnecessary.

A generally U-shaped tube 19 is associated with the discharge end 20 of nozzle 18. Tube 19 preferably includes a pair of generally vertical and parallel legs 21 and 22 interconnected by a generally horizontal portion 23. The tube 19 is hollow with leg 22 shorter than leg 21 for reasons to be discussed shortly. Thus, discharge end 20 of nozzle 18 discharges into longer leg 21. Shorter leg 22 is preferably open as shown. While nozzle 18 and U-tube 19 are shown located below the tank 10 they could be located elsewhere. It is preferable that the nozzle and U-tube be located below the tank.

A drain 24 may be associated with horizontal portion 23, controlled by a suitable normally closed control valve 25, for draining off water from tube 19. The outlet end 26 of drain 24 may be connected to a sewer or the like (not shown) for discharging the drained-off water. The drain valve 25 should be opened and the U- tube drained before each operation to insure that the U-tube is filled with the higher density liquid. Since the U-tube may contain hydrocarbons, provisions should be made to couple the outlet 26 to a suitable disposal system.

The height and inner dimensions of tube 19 are preferably chosen to provide a suitable capacity for water therein to carry out the techniques of my invention. For example, the inner diameter of portions 22 and 23 may be 2 inches and the inner diameter of portion 21 may be 4 inches. The height of leg 21 may be 24 inches or so and the height of leg 22 may be 18 inches or so. Thus, leg 21 extends a short distance (e.g., 6 inches) above the upper limit of leg 22 for the following reasons:

As can be seen in the drawing, a first dotted line X is shown at the upper end of leg 21. This line X is at the same level as the upper end of leg 22. In other words, when water is present in tube 19, it seeks both level X in leg 21 and level 27 of leg 22.

In operation, valve 15 is opened and water 11 is drained from tank 10. The water passes out of drain 13, through pipe 15 and discharges past nozzle 18 into leg 21 of tube 19. Valve 25 is opened and water thus drains off through the outlet end 26 of drain 24. The water present in tube 19 seeks both levels X and 27 in legs 21 and 22, respectively. While it is possible to operate by draining the tank through drain, it is preferable that the. tank be drained by overflowing the end 27 of the U- tube. This procedure will maintain both legs of the U tube filled with the higher density liquid. The drain 27 can be connected to a sewer providing the sewer is of sufficient size to prevent back pressure build-up in the U-tube.

When the second liquid 12, that is, the liquid of lower density than liquid ll--hydrocarbon in the example shown--appears on top of the water in leg 21, level X in the drawing, the nozzle 18 automatically senses this backup of liquid and shuts off thus stopping the draining of liquids from tank in which case the liquid remaining therein is essentially hydrocarbon free from water and other sediments.

In the example shown, the hydrocarbon may have a gravity 0.75 or less that of the water. Thus, it appears on top of the U-tube water seal X. Therefore, the techniques of my invention are generally applicable to most liquids of differing densities, the only requirement being that the density of one liquid be sufficiently lower than the density of the other so that it can be sensed by known nozzle equipment.

Various materials may be used to construct the equipment disclosed herein. Certain materials, as for example, aluminum or brass, may not be adequate for nozzle 18 when the apparatus of my invention is to be installed in areas susceptible to fires. Further, various control valves and gauges may be provided; valve may ,be eliminated, if desired, since nozzle 18 also serves as a drain valve. Conventional liquid strainers or the like may be provided where necessary to prevent fouling of various portions of the equipment disclosed herein, as, for example, valve seats (not shown) or the like. The length of discharge end is chosen (or end 20 is so extended therein) so that it may be extended into leg 21 above level X but in a position adapted to be contacted by the lower density liquid (i.e. level X).

In summary, the apparatus and method of my invention provides a technique for draining hydrocarbon storage tanks or the like of water and bottom sediment. It may be automatically drained, as by valve 15' and/or nozzle 18, and does not require an operator to remain in attendance to shut off the drain. The techniques disclosed herein reduce the potential for stored produce losses and environmental contamination through excess losses of hydrocarbon or the like to effluent collection system.

Although the techniques of my invention may be applied to the storing of any two-phase liquids, it has particular application to the drawing of hydrocarbon storage tanks which tend to form layers of emulsion and water at the bottom of the stored liquid. This material must be removed to prevent process upsets and product contamination.

I claim as my invention:

1. Apparatus for storing liquids of different densities comprising:

a storage tank adapted to contain said liquids therein;

an outlet associated with said tank for draining the higher density liquid therefrom;

outlet shutoff means associated with said outlet and in liquid communication therewith adapted to shut off said outlet and thus stop the draining of said tank; and

changing liquid density sensing means associated with said outlet shut-off means for sensing the change in density of said liquids when said lower density liquid begins to drain from said tank and shutting off said outlet shutoff means, the sensing means including a generally U-shaped tube associated with said shut-off means and having a pair of generally vertically disposed open-ended inlet and outlet legs, said inlet leg being longer than said outlet leg, and in liquid communication with both said shut-off means and said outlet leg.

2. The apparatus of claim 1 wherein said shut-off means includes a nozzle discharging into said inlet leg and the height of said outlet leg with respect to said inlet leg is below the nozzle of said shut-off leans.

3. The apparatus of claim 2 wherein said shutoff means includes actuating means for shutting off said nozzle upon back-up of said higher density liquid through said nozzle.

4. Apparatus for storing liquids of different densities comprising:

a storage tank adapted to contain said liquids therein;

an outlet associated with said tank for draining the higher density liquid therefrom, the outlet being in the bottom wall of said tank;

outlet shutoff means associated with said outlet and in liquid communication therewith adapted to shut off said outlet and thus stop thedraining of said tank, the shut-off means including a drain pipe in liquid communication therewith, said drain pipe having a first generally vertical portion extending downwardly therefrom and a second generally horizontal portion; and

changing liquid density sensing means associated with said outlet shut-off means for sensing the change in density of said liquids when said lower density liquid begins to drain from said tank and shutting off said outlet shutoff means, the sensing means being associated with a nozzle in liquid communication with said second generally horizontal portion, and including a generally U-shaped tube below the lowermost level of said tank and having generally vertical parallel inlet and outlet legs, said nozzle extending into said inlet leg at a level above the-uppermost level of said outlet leg.

5. The apparatus of claim 4 including a drain outlet associated with said tube for draining liquids therefrom.

6. The apparatus of claim 4 wherein said sensing means includes means associated with said nozzle for selectively passing and stopping the flow of liquids therethrough. 

1. Apparatus for storing liquids of different densities comprising: a storage tank adapted to contain said liquids therein; an outlet associated with said tank for draining the higher density liquid therefrom; outlet shutoff means associated with said outlet and in liquid communication therewith adapted to shut off said outlet and thus stop the draining of said tank; and changing liquid density sensing means associated with said outlet shut-off means for sensing the change in density of said liquids when said lower density liquid begins to drain from said tank and shutting off said outlet shutoff means, the sensing means including a generally U-shaped tube associated with said shut-off means and having a pair of generally vertically disposed open-ended inlet and outlet legs, said inlet leg being longer than said outlet leg, and in liquid communication with both said shut-off means and said outlet leg.
 2. The apparatus of claim 1 wherein said shut-off means includes a nozzle discharging into said inlet leg and the height of said outlet leg with respect to said inlet leg is below the nozzle of said shut-off means.
 3. The apparatus of claim 2 wherein said shutoff means includes actuating means for shutting off said nozzle upon back-up of said higher density liquid through said nozzle.
 4. Apparatus for storing liquids of different densities comprising: a storage tank adApted to contain said liquids therein; an outlet associated with said tank for draining the higher density liquid therefrom, the outlet being in the bottom wall of said tank; outlet shutoff means associated with said outlet and in liquid communication therewith adapted to shut off said outlet and thus stop the draining of said tank, the shut-off means including a drain pipe in liquid communication therewith, said drain pipe having a first generally vertical portion extending downwardly therefrom and a second generally horizontal portion; and changing liquid density sensing means associated with said outlet shut-off means for sensing the change in density of said liquids when said lower density liquid begins to drain from said tank and shutting off said outlet shutoff means, the sensing means being associated with a nozzle in liquid communication with said second generally horizontal portion, and including a generally U-shaped tube below the lowermost level of said tank and having generally vertical parallel inlet and outlet legs, said nozzle extending into said inlet leg at a level above the uppermost level of said outlet leg.
 5. The apparatus of claim 4 including a drain outlet associated with said tube for draining liquids therefrom.
 6. The apparatus of claim 4 wherein said sensing means includes means associated with said nozzle for selectively passing and stopping the flow of liquids therethrough. 